1. Field of the Invention
This invention relates generally to clothes washing machines, and more particularly, to a method and system for detecting a tub imbalance condition in a washing machine.
2. Description of Related Art
Residential and commercial clothes washing machines are well known. A generally cylindrical tub or basket for holding the clothing and other articles to be washed is rotatably mounted within a cabinet. Typically, an electric motor drives the tub. During a wash cycle, water and detergent or soap are forced through the clothes to wash them The detergent is rinsed from the clothes, then, during one or more spin cycles, the water is extracted from the clothes by spinning the tub.
One way of categorizing washing machines is by the orientation of the washing machine tub. Conventional, vertical-axis washing machines have the tub situated to spin about a vertical axis. Articles to be washed are loaded into the tub through a door, which is usually situated on the top of the washing machine. A vertical-axis washing machine tub includes an agitator situated therein, which cleans clothes by pushing and pulling them down into the water. A motor typically drives the agitator, in addition to spinning the vertically-oriented tub during spin cycles. The motor usually operates at a constant speed, and a series of gears or belts are configured to drive the proper component at the proper time during each washing machine cycle.
Horizontal-axis washing machines, having the tub oriented to spin about an essentially horizontal axis, do not include an agitator, and a variable-speed motor drives the tub. During wash cycles, the tub of the horizontal-axis washing machines rotates at a relatively low speed. The rotation speed of the tub is such that clothes are lifted up out of the water, using baffles distributed about the tub, then dropped back into the water as the tub revolves.
Both vertical and horizontal-axis washing machines extract water from clothes by spinning the tub, such that centrifugal force extracts water from the clothes. It is desirable to spin the tub at a high speed and extract the maximum amount of water from the clothes in the shortest possible time, thus saving time and energy. The distribution of the clothes about the periphery of the tub affects the washing machine""s ability to spin the tub at a high speed.
Vertical-axis washing machines are especially susceptible to imbalance problems. Several factors contribute to this predicament. For instance, when a wash or rinse cycle completes and the water is drained from the tub, the clothes are gathered at the bottom of the tub, not distributed about the entire tub. In conventional washing machines, the tub typically is not perfectly cylindrical; but rather, includes a draft. When the tub spins, the clothes will xe2x80x9ccreepxe2x80x9d up the sides of the tub. However, since a constant speed motor typically drives the vertically-oriented tub, the motor quickly ramps the tub up to the full spin speed. There is little chance for the clothes to distribute about the periphery of the tub, so they creep up the tub""s sides in an unbalanced fashion.
The unbalanced, spinning tub vibrates within the cabinet. In conventional vertical-axis washing machines, if the vibration is too severe, the tub will trip a switch mounted inside the cabinet, stopping the tub""s rotation and activating a tub-imbalance alarm A user then manually redistributes the wet clothes within the tub, and restarts the spin cycle.
Horizontal-axis washing machines typically are less vulnerable to tub imbalances. As discussed above, the tub in a horizontal-axis machine is driven by a variable speed motor. This allows the inclusion of a xe2x80x9cdistributionxe2x80x9d cycle, wherein the tub is rotated faster than the rotation speed of a wash cycle, but slower than in a spin cycle. The tub rotation speed is gradually increased, until the clothes begin to xe2x80x9cstickxe2x80x9d to the sides of the tub due to centrifugal force. The slower rotation speed allows the clothes to more evenly distribute about the sides of the tub. Once the clothes have been distributed about the tub, the speed is increased to a fill spin speed to extract the water from the clothes.
Even though horizontal-axis washing machines may be less prone to tub imbalances, they are not immune to tub imbalance problems. If the clothes do not evenly distribute during the distribution cycle, the unbalanced load within the tub will cause unwanted vibrations as the tub rotates. Rather than applying all of the motor""s power to spinning the tub at the highest possible speed, power is wasted in tub movement and cabinet vibrations.
Thus, it is desirable to detect the presence of an imbalance condition in a rotating tub, and take corrective action. However, prior art methods for detecting imbalance conditions have been largely unsatisfactory. The present invention addresses these, and other, shortcomings associated with the prior art.
In one aspect of the present invention, a method of detecting an imbalance condition in a rotating washing machine tub includes receiving an indication of a power level required to maintain a given washing machine rotation speed, and comparing the required power level to a predefined standard power level associated with the given rotation speed. In response to the comparison, a tub imbalance condition may be detected.
In another aspect of the present invention, a system for detecting an imbalance condition for a rotating washing machine tub includes a processor and a memory accessible by the processor. A standard power level associated with a given rotation speed is stored in the memory, and a speed detection device indicates the rotation speed of the washing machine tub. The processor is programmed to calculate a power level required to achieve the given washing machine rotation speed indicated by the speed detection device, and compare the required power level to the predefined standard power level to detect a tub imbalance condition The power level required to achieve the given rotation speed may be based on the output of a controller.